Long-term follow-up data are provided for a previously reported study of patients with membranous glomerulonephritis (MGN), nephrotic syndrome, and renal function impairment. Nine patients were treated with cyclophosphamide (1 to 2 mg/kg) and six of these received concurrent prednisone; they are compared with 17 concurrent controls (14 of whom had received prednisone at some time). The mean follow-up is 83 +/- 13 months in the treated patients and 64 +/- 7 months in the controls. Of the nine treated patients, four achieved a complete remission from the nephrotic syndrome (proteinuria less than 0.5 g/d), and five a partial remission (proteinuria decreased by at least 50% and to less than 3.5 g/d). One of the nine treated patients and 10 of the 17 controls have reached end-stage renal disease (ESRD) (P less than 0.05). Nine of the controls reaching ESRD had persistent nephrotic syndrome, whereas of the seven controls who have not yet reached ESRD, only two have persistent nephrotic syndrome (chi 2, P less than 0.02). There have been four relapses in three treated patients, and three of the four have responded to repeat therapy. One patient refused full therapy and remains nephrotic. Life-table analysis demonstrates significantly increased survival from ESRD in treated patients as compared with controls (P = 0.04).